Groundwind Notes

Field notes on wind checks

Tuning the Wind: How Your Powder Checks Fix the Forecast

The forecast tells you what the wind is doing 10 metres in the air, across a massive 2.5 km square. But your powder tells you what the air is doing right here, right now. Groundwind weighs one against the other to figure out exactly how the local air deviates from the forecast.

Here is how many puffs it takes to tune your map, where to take them, and how long they last.

By Gavan. 13 October 2026, a 5-minute read.

What a Check Does

Puff your powder, tap Sharpen, and log the wind's direction and how hard it's blowing. That single check works at three different scales:

  • Right here, right now: The wind map immediately updates to match what you felt, and your scent cone swings to match it.
  • Across the area: Once you log two or more checks, the app calculates how the broader air above the trees deviates from the forecast. It then shifts the wind streaks and scent cones across a 2 to 3 km radius around you.
  • Over the season: Every check teaches the app how the air behaves in that specific terrain—like cold air draining or a lake breeze pushing in. The map applies that lesson to similar spots, and lets it go over a couple of weeks.
One check: Sharpen, the powder's way, how hard
The cone turns to what you felt

When to Trust the Forecast vs. Your Powder

We measured our terrain wind models against 1,100 weather stations over 330,000 hours of legal hunting light (ECCC; HRDPS; Open-Meteo). The takeaway? Forecasts do a great job in the open, but under the canopy at head height, the woods add their own spin.

  • In a strong breeze: The forecast is rarely far off. One weird, swinging puff of powder shouldn't overrule it.
  • In light air: The forecast's direction is only a loose guide. This is when your powder checks matter most.

Why You Need More Than One Puff

Powder is unpredictable. At our own sits, puffs taken just minutes apart swung by nearly 50°—and even more in light air. Because a single puff is rough, Groundwind lets your checks outvote the forecast only when multiple puffs agree with each other.

Where the powder went · the lake shore at Pickle, 30 Sept at dusk

Five puffs in 85 minutes on the lake shore at dusk, each pointing where the powder went: southeast at 17:32, east at 18:01 and 18:53, northwest at 18:27 and southwest at 18:56. NSW 17:3218:01 · 18:5318:2718:56
Five puffs in 85 minutes
Light air at dusk: average these and you get a wind that isn't there

Four puffs and the tuned wind · the air going left to right

The forecast points straight across. Four puffs scatter about 35° to its left. The tuned wind points between them, part of the way from the forecast toward the puffs. you forecast your puffs tuned
Four puffs, about 35° left of the forecast
The tuned wind goes part of the way: further in light air, and when they agree

How Many Puffs Does It Take?

It depends on how hard the forecast says the wind is blowing. The app's card will count for you and tell you when the air is "settled," but here is the general rule:

  • Light air (6 km/h or less): 2 puffs
  • Light breeze (10 km/h): 4 puffs
  • Moderate (14 km/h): 7 puffs
  • Breezy (18 km/h and up): The forecast is seldom far off; your puffs will mostly just confirm it.
The check card after a second check in light air. It reads: This sit's 2 checks: the air above the trees runs 15° left of the forecast at about 82% of its speed. Then: 1 more puff, spaced out, and the air here is settled: in this wind about 3 is what it takes to trust your checks over the forecast.
The card after a second check, 7 km/h
One more puff settles it

Most of the time, the forecast is close. But on the bad days—when the forecast is off by 45° or more—taking enough puffs is what pulls the map back to reality.

When the forecast was over 45° off · how often the puffs put it right

Of the virtual sits where the forecast was more than 45° off, the share the puffs put right: none with no puffs, 38% with two, 57% with four and 83% with eight. None0%2 puffs38%4 puffs57%8 puffs83%
12,000 virtual sits at the stations, in legal light
Puffs as rough as real ones, ±60°

Field Rules: Where and When to Puff

The second check, 300 m from the first
The card asks for one under the trees next

Field rules

  • Two places, not one: Take your second puff at least 50 m away from your first. Doing one in the open (like a bog or cutline) and one under the trees tells the app how much of the higher air is actually reaching the ground.
  • Puff as you walk: Each check is tied to the exact minute it was taken. A check from your walk-in still helps map your sit hours later.
  • Check when the light changes: As the sun rises or sets, the air switches between draining and rising. When this happens, your old checks no longer apply.
  • Tell the app if it holds: If the wind is steady, tap same as a while ago and your check will be trusted for twice as long.
  • Watch the canopy: If it's calm where you sit but the canopy is swaying, tap treetops moving, calm here. The treetops are a steadier read than powder in a gusty spot.

How Long Does a Check Last?

Wind changes, and so do your checks. Half of a check's influence fades in under two hours (or four if you tell the app the wind held). After a day, it completely resets.

How much of a check still holds · hours after it

Share of a check's correction still holding, by hours after it. Direction: 60% after an hour, 45% after two, about a quarter after six. Speed: 72%, 57%, then about a third. The app's fade, drawn as lines, runs through the stations' measurements, drawn as dots. 0%50%100% 0 h1 h2 h3 h4 h5 h6 h direction speed
Dots: the stations, in legal light · lines: the app's fade
Most of a check's say is gone in a few hours: check again

Checks are also strictly local. They tune your specific patch of bush, not the next lake over. Move 10 km away and only about a fifth of what a check learned still holds.

Every Check Teaches the Map

Every time you log a puff, Groundwind keeps score of what the forecast said versus what you actually felt. If you opt in, your anonymous checks are sent back to us. That is how we measure performance, and how Groundwind learns where it's wrong so it can get it right next time.

On 10 October, on the valley floor at Searchmont, the forecast had the wind from the south-southeast. My powder said it was coming from the northwest.

Tune the wind on your own ground.

Groundwind takes the HD forecast down to head height over the 1 m LiDAR ground and every stand of trees, and draws your scent cone on it. Every puff you log tunes it to the air that's really there. It works with no service.

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Where the numbers come from

The station figures are our own measurements, made on public data. Here is where that data comes from, and the book on weighing measurements against a forecast.